Current viscous-damped rotator design and technology employ a cylindrical or conical rotor attached to a shaft that rotates within a housing having a cylindrical or conical chamber (rotor cavity) that is filled with a viscous fluid (this device is sometimes referred to as a "rotor motor"). The rotor motor acts as a brake or dampener to control the rotational speed of the stream distribution or rotor plate. The dampening or resistance that impedes rotation comes from the high forces required for shearing the viscous fluid molecules. This shearing takes place between a moving boundary layer, (molecules of fluid attracted to the rotor surface), and stationary neighboring fluid molecules (molecules attracted to the stator or housing surface) in the rotor cavity.
If the viscous fluid molecules separate from neighboring molecules and a less viscous foreign substrate fills the gap between molecules, the rotor may become free spinning, i.e., it may rotate at a speed approaching that which would occur in the absence of any viscous dampening. In the rotor cavity, air is the predominant substrate that may fill this thin gap. It is believed that as the rotor turns, air in the rotor cavity begins to thinly distribute itself all the way around the rotor until it grows large enough (or spreads itself thin enough) to separate the viscous fluid molecules all around the cylindrical surface of the rotor. In effect, a cylindrical sleeve of air is formed in the much thicker viscous fluid. The result is that the viscous fluid molecules no longer shear, and the dampening or braking effect becomes negligible.
An obvious solution would be to prevent air from ever entering the rotor housing and, more specifically, the rotor cavity. This however has proven to be unobtainable and probably not practical. Moreover, closer evaluation and testing has shown that very small amounts of air are of little consequence. The real problem comes to light when there is too much air present, and at the wrong location within the rotor cavity. In fact, the volume of air is less significant than its location within the cavity. For example, a large bubble at the top of the cavity is not a problem, but a smaller air volume "smeared" around the rotor may indeed be problematic. The goal then is two-fold: to have as little air as possible in the rotor cavity, and then to manage any air that is present. This invention focuses on the management of air present within the rotor cavity.
A first air management technique incorporates air management features into the rotor design per se. Movement of the air is accomplished by manipulating the geometry of the rotor. It has been discovered that changing the geometry of the rotor to have one or more fins protruding outwardly to a point closely adjacent the interior surface of the housing, i.e., the surface defining the rotor cavity, appears to manage most of the air in an efficient manner. As the rotor rotates, high and low pressure areas are created in front of and behind the rotor fins respectively. The much thinner air rushes to the low pressure area behind the rotor fin and trails in this low pressure wake. By staying in this wake as the rotor rotates, the leading edge of the rotor is able to penetrate pure viscous fluid, maintaining an area of fluid-to-fluid shearing, resulting in the dampening required for proper rotation. Over an extended period of usage, however, fluid can leak out leaving air/water in its place. In the event the volume of air is large enough to fill the entire low pressure area behind all elements of the rotor, thus allowing the leading edge to hit air rather than fluid, the result will be the loss of the viscous fluid shearing. Further refinement of the rotor design reveals that non-symmetrical fins will further enhance the volume of air that can be managed. By making one of two fins shorter, air traveling in the shorter fins radial wake has been moved inward, away from the path of the approaching longer fin. This results in the longer fin penetrating the fresh fluid required for proper shearing.
A third variation of this method utilizes a cylindrical rotor with one or more recesses to create low pressure pockets for the air to be contained. This can range from large lengthwise grooves or pockets to many thin shallow grooves or even dimples.
A second air management technique utilizes a rotating disk inside the rotor cavity. The disk could be a part of the rotor or axially spaced from the rotor. This disk acts as a "decoy," i.e., it attracts air to its surface rather than to the rotors surface. By making the disk's major diameter larger than the rotor, the disk has an increased shear rate due to its higher velocity, which produces a higher rate of boundary layer separation. This separation appears to create small eddy currents near the disk surface that attract the air. Air is thus continuously attracted to the moving disk the entire time rotation is occurring, allowing the desired viscous shearing to occur in the area between the rotor body and the housing surface. Perforating the thin disk also helps more air to be managed by creating small, low pressure pockets that attract and capture air as the disk rotates.
In the detailed description which follows, several different rotor designs are described, each of which is designed to efficiently manage air inside the rotor cavity so as not to degrade the viscous dampening function of the rotor motor.
Testing has shown that with this invention, a rotor will still operate properly with just 50% of the original fluid volume. This is most significant with micro rotators due the difficulty of purging all air from the small rotor housing during assembly.
Accordingly, in one aspect, the invention relates to an improvement in a rotary sprinkler comprising a nozzle and a rotatable stream distributor plate secured to one end of a shaft, wherein rotational speed of the stream distributor plate is controlled by a viscous damping arrangement including a rotor body on an opposite end of the shaft and located within a chamber at least partially filled with a viscous fluid, and wherein the rotor body is rotatable relative to a stator; the improvement wherein a disk is mounted within the chamber for rotation with the rotor body, the disk having an outside diameter greater than an outside diameter of the rotor body.
In another aspect, the invention relates to an improvement in a rotary sprinkler comprising a nozzle and a rotatable stream distributor plate, wherein rotational speed of the stream distributor plate is controlled by a viscous damping arrangement including a rotor arranged within a chamber at least partially filled with a viscous fluid, and wherein the rotor is rotatable relative to a stator; the improvement wherein the rotor includes a hub and at least one fin projecting therefrom.
In still another aspect, the present invention relates to a rotational speed viscous dampening device comprising a housing, a shaft having one end located in the housing and rotatable relative thereto, and a rotor body on the one end of the shaft with viscous fluid at least partially filling the housing, the improvement comprising means for managing air within the housing so that the air does not substantially interfere with viscous shearing of molecules of the viscous fluid between the rotor body and an interior wall of the housing.
In still another aspect, the invention relates to a rotary sprinkler comprising a nozzle and a rotatable stream distributor plate secured to one end of a shaft, wherein rotational speed of the stream distributor plate is controlled by a viscous damping arrangement including a rotor on an opposite end of the shaft and arranged within a chamber at least partially filled with a viscous fluid, and wherein the rotor is rotatable relative to a stator; the improvement wherein the rotor includes a center hub with an annular disk at one end thereof, and a fin extending axially along the center hub between the disk and an opposite end of the center hub.
In still another aspect, the invention relates to a rotary sprinkler comprising a nozzle and a rotatable stream distributor plate secured to one end of a shaft, wherein rotational speed of the stream distributor plate is controlled by a viscous damping arrangement including a rotor on an opposite end of the shaft and arranged within a chamber at least partially filled with a viscous fluid, and wherein the rotor is rotatable relative to a stator; the improvement wherein the rotor includes one or more air accumulating pockets formed therein.
Other features of the invention will become apparent from the detailed description which follows.